refactor: DRY cleanup — extract shared helpers, remove duplication across tools, LSP, overlays, and runtime

Eliminate ~500 lines of duplicate code across 31 files by extracting
shared functions, helpers, and consolidating repeated patterns.

Highlights:
- Toast helpers (toast_info/success/warning/error) on AppStateRest
- push_event() helper for turn-event queue (19 callers consolidated)
- log_write_edit_tool() shared fn (turn.rs + engine.rs ~50 lines saved)
- resolve_api_key() shared fn (spawn.rs + provider.rs)
- LSP call_positional() helper on LspClient
- lsp_cursor_params() shared schema for 4 tool files
-overlay_block() helper for consistent overlay title/border styling
- cycle_selected_index(), path_not_found/a_directory() helpers
- mark_dirty(), save_settings() on AppStateRest
- Remove redundant Err(e) => Err(e) arms in LSP tools
- Consolidate generate_workspace_tree (turn.rs → workspace.rs)
- Simplify background-review wrapper args in auto/mod.rs

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/zesdex-backend/src/view/overlays/bash.rs

@@ -1,4 +1,4 @@
-use ratatui::style::{Modifier, Style};
+use ratatui::style::Style;
 use ratatui::text::{Line, Span};
 use ratatui::widgets::{Block, Paragraph};
 use ratatui::Frame;
@@ -10,14 +10,7 @@ pub fn render(
     block: Block<'static>,
     state: &crate::app::state::rest::AppStateRest,
 ) {
-    let block = block
-        .title(Span::styled(
-            " Bash Jobs ",
-            Style::default()
-                .fg(Theme::ACCENT_ORANGE)
-                .add_modifier(Modifier::BOLD),
-        ))
-        .border_style(Style::default().fg(Theme::ACCENT_ORANGE));
+    let block = super::overlay_block(block, "Bash Jobs", Theme::ACCENT_ORANGE);
     let lines: Vec<Line> = state
         .session_runtime
         .as_ref()

crates/zesdex-backend/src/view/overlays/help.rs

@@ -1,5 +1,4 @@
-use ratatui::style::{Modifier, Style};
-use ratatui::text::Span;
+use ratatui::style::Style;
 use ratatui::widgets::{Block, Paragraph, Wrap};
 use ratatui::Frame;
 use crate::view::theme::Theme;
@@ -10,14 +9,7 @@ pub fn render(
     block: Block<'static>,
     _state: &crate::app::state::rest::AppStateRest,
 ) {
-    let block = block
-        .title(Span::styled(
-            " Help ",
-            Style::default()
-                .fg(Theme::INFO)
-                .add_modifier(Modifier::BOLD),
-        ))
-        .border_style(Style::default().fg(Theme::INFO));
+    let block = super::overlay_block(block, "Help", Theme::INFO);
     let content = crate::prompts::HELP_TEXT;
     let paragraph = Paragraph::new(content)
         .block(block)

crates/zesdex-backend/src/view/overlays/mod.rs

@@ -19,11 +19,29 @@ pub mod todo;
 pub mod usage;
 
 use ratatui::layout::Rect;
-use ratatui::style::Style;
+use ratatui::style::{Modifier, Style};
+use ratatui::text::Span;
 use ratatui::widgets::{Block, Borders, Clear};
 use ratatui::Frame;
 use super::theme::Theme;
 
+/// Decorate an overlay block with a styled title and matching border color.
+///
+/// Every overlay renders a `Block` with a title bar in its variant colour
+/// and a matching border — this helper centralises the `Span::styled` +
+/// `border_style` boilerplate that was duplicated identically in 14 overlay
+/// modules.
+pub fn overlay_block(block: Block<'static>, title: &str, color: ratatui::style::Color) -> Block<'static> {
+    block
+        .title(Span::styled(
+            format!(" {title} "),
+            Style::default()
+                .fg(color)
+                .add_modifier(Modifier::BOLD),
+        ))
+        .border_style(Style::default().fg(color))
+}
+
 /// Compute a centered rectangle within `area` at the given percentage width
 /// and height. The result is always at least 40 cols wide and 10 rows tall.
 pub fn centered_rect(area: Rect, percent_x: u16, percent_y: u16) -> Rect {

crates/zesdex-backend/src/view/overlays/settings.rs

@@ -1,4 +1,4 @@
-use ratatui::style::{Modifier, Style};
+use ratatui::style::Style;
 use ratatui::text::{Line, Span};
 use ratatui::widgets::{Block, Paragraph};
 use ratatui::Frame;
@@ -10,14 +10,7 @@ pub fn render(
     block: Block<'static>,
     state: &crate::app::state::rest::AppStateRest,
 ) {
-    let block = block
-        .title(Span::styled(
-            " Settings ",
-            Style::default()
-                .fg(Theme::PRIMARY)
-                .add_modifier(Modifier::BOLD),
-        ))
-        .border_style(Style::default().fg(Theme::PRIMARY));
+    let block = super::overlay_block(block, "Settings", Theme::PRIMARY);
     let lines = vec![
         Line::from(Span::styled(
             format!("  Provider:     {}", state.settings.provider),